You are in: Home › Census › Census Learning Zone › How is the census information processed ›

Census Learning Zone

How is the Census Information Processed?

For over a hundred years, armies of clerks sitting at desks compiled Census results by hand. They had to copy and collate information from the books filled in by the people who visited every home to record the details of each household member. It was 1911 when the first punched-card machines were used; this allowed information to be counted semi-automatically (these punched-card machines were the forerunners of the modern computer). But despite the introduction of electronic computers in 1961, the processing of Census forms was still a very labour-intensive operation. For instance, in 1991 almost all the forms from around Great Britain were sent to a processing centre at Hillington near Glasgow. There it took a team of 550 operators over a year to manually key-in the information from the forms to make a computerised record of the results.

In 1995 the United Kingdom Census Offices looked at how other countries captured information from their Census forms. For the 2001 Census it was decided that sophisticated scanners should be used to create digital images of each page of every form, and then to automatically capture the details that were written on these pages. Trials showed that the automatic recognition of hand-written ticks and characters had become very accurate and reliable. This Census, instead of more than 500 people being needed to look through every one of the 30 million United Kingdom forms and manually key details into the computer, the scanners rapidly captured over 500 million images of pages from the 2001 Census forms and extracted the desired information.

However, getting all this information into the computer is not a totally automated process. The automatic recognition software can be confused by what it reads and then has to rely on human intervention to decide on what should be entered.

A by-product of the scanning process was that a permanent microfilm record was produced containing all the images of all the pages of all the forms. This allowed the forms themselves to be destroyed at the end of the job, thus saving on the cost of storage, as microfilm takes up a fraction of the space required to store boxes of forms - instead of a warehouse only a large filing cabinet is needed. The personal information held on microfilm is kept secret for at least 100 years.

After the basic information has been captured from the Census forms, responses that are written in text have to be converted into codes that the computer can then use to count and collate. Again, in the past, the coding of information has been a labour-intensive process. For the 2001 Census clever coding software was developed that automatically took the captured text and converted it into codes. But the software is still not as intelligent as a human, and a large team of expert coders were still used to sort out the difficult cases (for example, when coding occupation, the computer may easily find a code for "Mathematics Teacher" but may struggle with "Learning Facilitator").

For the 2001 Census the capture and coding of details from the Census forms for the whole of the United Kingdom took place at Widnes in Cheshire, near Liverpool. At the warehouse, where the forms were sorted and stored, and at the processing centre, where data was captured and coded, about 1,500 people worked in two shifts to complete the capture and coding process in less than a year.

After the data has been captured and coded it is passed to the Census Statisticians who have devised automatic processes to make the information complete and consistent before it is finally used to produce the statistics that are available to organisations and individuals.

The millions of items of data compiled from the forms become statistics. These are counts that represent some characteristic that can be compared with other characteristics or manipulated in some other way. The job of the statistician is to put the information gathered into useful classes - like age bands, types of accommodation, employment groups and many others - and from them compile a highly detailed picture of the population of the United Kingdom. The statistics from the Census mainly take the form of tables showing one characteristic compared with another.

The statisticians use the information to highlight changes over a period of time. From the Census information gathered in 2001 they can see clearly how it compares with the 1991 Census and others before then.

The easiest trend to follow is the rise - and eventual fall - of the total population of Scotland. An unofficial Census in 1753 gave a total of 1,265,380. The first official Census in 1801 showed the population to be 1,608,420. A hundred years later, in 1901, the total had risen to 4,472,103, while the Census in 1991 counted 5.1 million people resident in Scotland. However, this is down on the highest recorded figure, which was 5,228,963 in 1971, and recent non-Census records predict that the population is continuing to decrease.

The delivery of these statistics allows other people whose job it is to provide or improve services such as schools, sports facilities, hospitals, roads, shops, factories and so on, to work out where these facilities are most needed and plan how to provide them for local communities.

Gàidhlig